1. Field of the Invention
The present invention relates to a detecting circuit, and specifically relates to a detecting circuit capable of detecting an abnormal state of a vibrating gyroscope.
2. Description of the Prior Art
FIG. 2 is a block diagram showing an example of a conventional vibrating gyroscope, which is the background of the present invention and whereto the present invention is applied. In the vibrating gyroscope 1, piezoelectric elements 3a and 3b for driving and detecting are formed on two side surfaces of a triangular prism-shaped vibrator 2, and a piezoelectric element 4 for feedback is formed on the other one side of the vibrator 2.
The piezoelectric element 4 for feedback is connected to the piezoelectric elements 3a and 3b through an oscillation circuit 5 and a phase-shifting circuit 6. Further, the piezoelectric elements 3a and 3b are connected to two input terminals of a differential amplifier circuit 7 consisting of, for example, a differential amplifier, respectively. Also, an output terminal of the differential amplifier circuit 7 is connected to an input terminal of a synchronous detection circuit 8 The phase-shifting circuit 6 is connected to the synchronous detection circuit 8 to detect an output of the differential amplifier circuit 7 in synchronism with a driving signal of the vibrator 2. Further, an output terminal of the synchronous detection circuit 8 is connected to a rectifying/amplifying circuit 9 for rectifying and amplifying an output of the synchronous detection circuit 8.
In the vibrating gyroscope 1 as shown in FIG. 2, the vibrator 2 is driven by self-excited vibration by a feedback loop such as the oscillation circuit 5 and the phase-shifting circuit 6. In this case, the two piezoelectric elements 3a and 3b generate similar sine wave signals. Consequently, output voltages of the differential amplifier circuit 7, the synchronous detection circuit 8 and the rectifying/amplifying circuit 9 become nearly 0 V, respectively.
Here, when the vibrator 2 is rotated around the shaft thereof, in response to the rotary angular velocity of the vibrator 2, the voltage of the sine wave signal generated in one of the two piezoelectric elements 3a and 3b becomes large, and the voltage of the sine wave signal generated in the other one becomes small. Consequently, a sine wave signal of a magnitude responding to the rotary angular velocity of the vibrator 2 is outputted from the differential amplifier circuit 7 Then, the sine wave signal outputted from the differential amplifier circuit 7 is synchronized-detected by the synchronous detection circuit 8, and is rectified and amplified by the rectifying/amplifying circuit 9. Accordingly, the vibrating gyroscope 1 can detect the rotary angular velocity by the output voltage from the deferential amplifier circuit 7, the synchronous detection circuit 8 or the rectifying/amplifying circuit 9. For this reason, the vibrating gyroscope 1 is used, for example, for attitude control of a motorcar
However, in the case where the vibrating gyroscope 1 of FIG. 2 is used, for example, for attitude control of a motorcar, the attitude control of the motorcar is required to be performed only after making sure that the vibrating gyroscope 1 is operated in normal state Because, for example, when the vibrating gyroscope is operated in an abnormal state such that a connection line connected to each piezoelectric element is disconnected or short-circuited, an abnormal signal is outputted from the vibrating gyroscope, and when the abnormal signal is used intact as a signal for control, a dangerous state sometimes takes place